Fuel grade alcohol (e.g., ethanol) distilled from grain (e.g., corn) has become increasingly popular as an alternative to gasoline. Additionally, ethanol has increased in popularity as a gasoline additive for formulating clean burning grades of gasoline for motor vehicles.
One method of producing ethanol includes using a corn dry-milling process. A typical corn dry-milling process consists of four major steps: grain handling and milling, liquefaction and saccharification, fermentation and distillation, and co-product recovery. Grain handling and milling is the step in which the corn is brought into the plant and ground to promote better starch to glucose conversion. Liquefaction is the step of converting solids such as starch to a flowable liquid producing oligosaccharides and saccharification is where the oligosaccharides are converted into single glucose molecules. Fermentation and distillation is the process of yeast or bacteria, or clostridia, for example, converting glucose into a biofuel or a biochemical, such as ethanol. Co-product recovery is the step in which the corn by-products are de-watered and made ready. There are many known chemical and biological conversion processes known in the art that utilize yeast, bacteria, or the like to convert glucose to other biofuels and biochemical components like ethanol, for example.
The recovery of alcohol, e.g., butanol, ethanol, etc., and natural co-products generally begins with the beer (spent fermentation broth) being sent to a distillation system. With distillation, ethanol is typically separated from the rest of the beer through a set of stepwise vaporizations and condensations. To produce fuel grade ethanol, more than one interconnected distillation column is typically used to progressively purify the ethanol product. In a typical ethanol distillation process, a beer column receives beer and produces an intermediate ethanol vapor. A rectifier column receives the intermediate ethanol vapor from the beer column and produces 190 proof or 95% pure ethanol vapor. A third, side stripper column receives bottoms from the rectifier column and then produces an intermediate ethanol overhead vapor that is further purified by the rectifier column. The ethanol free bottoms from the side stripper column can be used to formulate cook water for the fermentation portion of the process. Because of the physical properties of an ethanol water solution, a distillation process can only practically produce an ethanol water solution that is approximately 95% ethanol and 5% water. A dehydrator is used to remove most of the remaining water to produce higher purity product. The dehydrator receives the 95% ethanol vapor and removes nearly all of the remaining water to produce ethanol having a water content typically of less than about 1.0%. A dehydrator may contain beads of material that attract or retain water molecules to a greater degree than ethanol molecules.
A fuel grade ethanol distillation process like the one described above also produces co-products. To that end, the beer less the alcohol extracted through distillation is known as whole stillage, which contains a slurry of the spent grains including corn protein, fiber, oil, minerals, and sugars as well as spent fermentation agent. These byproducts are too diluted to be of much value at this point and are further processed to provide the dried distiller's grains with solubles (DDGS).
In typical processing, when the whole stillage leaves the distillation column, it is generally subjected to a decanter centrifuge to separate insoluble solids or “wet cake”, which includes mostly fiber, from the liquid or “thin stillage”, which includes, e.g., protein, fine fiber, oil, and amino acids. After separation, the thin stillage moves to stillage evaporators to boil away moisture, leaving a thick syrup that contains soluble (dissolved) solids. The concentrated syrup can be mixed with the wet cake, and the mixture may be sold to beef and dairy feedlots as distillers wet grain with solubles (DWGS). Alternatively, the wet cake and concentrated syrup mixture may be dried in a drying process and sold as distillers dried grain with solubles (DDGS). The resulting DDGS generally has a crude protein content of about 32% and is a useful feed for cattle, other ruminants, and monogastric animals due to its protein and fiber content. The resulting product is a natural product.
A typical ethanol production process requires significant energy input as well as a significant amount of process water. It would be beneficial to provide a method and system for producing ethanol that conserves energy and water while utilizing waste heat from the stillage evaporators to heat other portions of the process.